Habermas seeks to renew our understanding of "legitimacy" and "legality" by including their relationship and problematicism within a concept of law that is exclusively relevant to democratic processes. We suggest here thinking about this concept in three phases: first: defending legal modernity as a horizon for democratic self-legislation, second: by looking at legitimacy as a result of democratic processes, third: presenting the issue of legality as an issue related to democratic processes and in a dependent relationship with them. Finally, the author insists on the legal-philosophical contributions that this theory has made to rethink our legal modernity. The issues surrounding the issue of legitimacy and legality are still the focus of contemporary reflections in legal philosophy, so if we can admit that the problem involves a long and interesting history in which large sections of Western legal philosophy are drawn, then our contemporary philosophical tools, as well as our democratic experiences, seem to us today More conducive to understanding these issues intellectually. The benefit that Habermas's theory of legitimacy and legality inspires us with comes from his way of understanding law. Therefore, it is necessary - first of all - to clarify this concept before we can consider how it extends thereafter on the axis of legitimacy and finally on the axis of legality.